Forecasting the Major Influences of Predation and Environment on Cod Recovery in the Northern Gulf of St. Lawrence

Nicolas Bousquet,Mike O Hammill,Emmanuel Chassot,Daniel E Duplisea,Francesco Pappalardo

doi:10.1371/journal.pone.0082836

Abstract

The northern Gulf of St. Lawrence (NGSL) stock of Atlantic cod (Gadus morhua), historically the second largest cod population in the Western Atlantic, has known a severe collapse during the early 1990 s and is currently considered as endangered by the Committee on the Status of Endangered Wildlife in Canada. As for many fish populations over the world which are currently being heavily exploited or overfished, urgent management actions in the form of recovery plans are needed for restoring this stock to sustainable levels. Stochastic projections based on a statistical population model incorporating predation were conducted over a period of 30 years (2010–2040) to assess the expected outcomes of alternative fishing strategies on the stock recovery under different scenarios of harp seal (Pagophilus groenlandicus) abundance and environmental conditions. This sensitivity study shows that water temperature is key in the rebuilding of the NGSL cod stock. Model projections suggest that maintaining the current management practice under cooler water temperatures is likely to maintain the species in an endangered status. Under current or warmer conditions in the Gulf of St. Lawrence, partial recovery might only be achieved by significant reductions in both fishing and predation pressure. In the medium-term, a management strategy that reduces catch could be favoured over a complete moratorium so as to minimize socio-economic impacts on the industry.

Highlights

The global expansion of world fisheries has sequentially led to the intense and/or over-exploitation of the majority of world’s major fish stocks, with only 1% undergoing some form of recovery from depletion [1,2,3,4]
Our findings provide insights into how the combined effects of the physical environment and trophic interactions can affect the outcomes of fishing management strategies aimed at rebuilding depleted stocks
Modelling results indicate that the northern Gulf of St. Lawrence (NGSL) stock recovery will probably take a long time and is strongly dependent on water temperature conditions, followed by seal predation, and fishing strategies

Summary

Introduction

The global expansion of world fisheries has sequentially led to the intense and/or over-exploitation of the majority of world’s major fish stocks, with only 1% undergoing some form of recovery from depletion [1,2,3,4]. The complexity of population dynamics responses to management actions at low population sizes has been highlighted, through past fishery experiences, by the ability of stocks to rebuild to former levels of abundance [5,7,8,9]. Processes such as depensation, higher demographic stochasticity, and potential genetic changes in vital rates might affect the recovery of depleted stocks [10,11,12]. Multispecies interactions, predator pits (i.e., where predation probability decreases above and below an intermediate level of the prey abundance), as well as oceanographic and environmental conditions have been shown to affect the productivity and rate of recovery for some fish populations [5,13]

Methods

Results

Conclusion